The invention provides for a polyvalent protein complex (PPC) comprising two polypeptide chains generally arranged laterally to one another. Each polypeptide chain typically comprises 3 or 4 "v-regions", which comprise amino acid sequences capable of forming an antigen binding site when matched with a corresponding v-region on the opposite polypeptide chain. Up to about 6 "v-regions" can be used on each polypeptide chain. The v-regions of each polypeptide chain are connected linearly to one another and may be connected by interspersed linking regions. When arranged in the form of the PPC, the v-regions on each polypeptide chain form individual antigen binding sites.
